1. Technical Field
The present invention relates to electric vehicles and a method of control.
2. Background Art
The term “electric vehicle” used herein encompasses battery electric vehicles (BEV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV).
A BEV includes an electric motor, wherein the energy source for the motor is a traction battery. The BEV traction battery is re-chargeable from an external electric grid. The BEV traction battery is in effect the sole source of on-board energy for vehicle propulsion.
A HEV includes an internal combustion engine and an electric motor, wherein the energy source for the engine is fuel and the energy source for the motor is a traction battery. The engine is the main source of energy for vehicle propulsion with the HEV traction battery providing supplemental energy for vehicle propulsion (the HEV traction battery buffers fuel energy and recovers kinematic energy in electric form).
A PHEV differs from a HEV in that the PHEV traction battery has a larger capacity than the HEV traction battery and the PHEV traction battery is re-chargeable from the grid. The PHEV traction battery is the main source of energy for vehicle propulsion until the PHEV traction battery depletes to a low energy level at which time the PHEV operates like a HEV for vehicle propulsion.
Many electric vehicles include an auxiliary battery for providing energy to vehicle accessory loads. Typically, during normal vehicle operation, the traction battery supplies energy to the auxiliary battery in order to maintain the auxiliary battery at a fully charged state (e.g., 100% state of charge (SOC)).
A problem with the traction battery supplying energy to maintain the auxiliary battery at the fully charged state is that this energy is lost for vehicle propulsion until recovered. Further, the amount of lost energy can be exacerbated as the auxiliary battery may not always be charged at most efficient operating points. The lost energy is generally problematic for electric vehicles as efficiency is critical for optimal performance and evaluation. This is especially a problem for a BEV in that the BEV essentially cannot recover the lost energy until the vehicle is connected to the external electric grid.